What GSM actually measures
GSM stands for grams per square metre — the weight of a single square metre of fabric. On non-woven bags it is the single most consequential specification you will choose, because it drives feel, strength, print quality, and unit cost all at once.
PP non-woven fabric is manufactured from polypropylene pellets extruded into fibres and spun into a web. GSM is the outcome of how much polymer is laid down per square metre, not a grade label applied afterwards. A 40 GSM fabric uses roughly half the polymer of an 80 GSM fabric of the same dimensions.
The practical GSM bands
40–50 GSM is the light end of the spectrum. Bags in this range feel thin and slightly papery, but they are cheap and they print cleanly because the surface is smooth and relatively flat. They suit lightweight retail goods — accessories, small apparel, promotional giveaways — where the bag's job is branding rather than load-bearing.
60–80 GSM is the workhorse band for B2B non-woven packaging. It has enough body to stand upright on a shelf, holds a heat-sealed handle without splitting, and survives repeated customer reuse. Most supermarket and pharmacy bag programmes land here.
90–120 GSM is heavy-duty territory. This fabric is used where the bag carries weight — grocery produce, hardware, multi-item purchases — or where the brand wants a premium, structured feel. It costs more per piece and resists print saturation, so artwork needs lighter coverage or a different print approach.
Matching GSM to what the bag carries
Start from the load, not from the price. A bag carrying 8 kg of grocery produce will need a reinforced handle construction and a heavier fabric than a bag carrying a single shirt, even if both are sold in the same retail environment.
For heavy grocery loads we typically specify 80 GSM with a reinforced die-cut handle and an ultrasonic-welded seam on the gusset. For pharmacy dispensing — where bags are light but need to look clinical and professional — 50 GSM with a clean white substrate is enough.
A useful rule: every 20 GSM of additional weight adds roughly 15–20% to the base fabric cost of the bag. That is a meaningful percentage on high-volume programmes, so it is worth being precise about whether you need the strength at all.
How GSM interacts with printing
Heavier fabric is not simply a stronger version of lighter fabric. The same ink behaves differently across GSM bands because of the difference in surface texture and absorbency.
On 40–50 GSM you get bright, saturated, high-contrast flexo print — the substrate is smooth and the ink sits on top. On 90–120 GSM the surface is more textured, so ink sinks into the valleys and the result reads slightly muted. Pantone matching is harder at the heavy end for the same reason.
If you are specifying a critical brand colour on a heavy fabric, request a physical Pantone strike-off before the production run. It costs a few days and removes the most common cause of a rejected bulk order.
What to write into your specification
Specify GSM as a minimum with an acceptable tolerance, not as an exact target. A realistic tolerance on a spun non-woven is ±5 GSM, and stating that explicitly prevents a dispute at goods-in.
A workable line reads: minimum 60 GSM, ±5 GSM tolerance, PP spun-bond non-woven, white substrate unless otherwise specified, suitable for four-colour flexo printing.
Pair that with a handle tensile requirement. A bag that passes the GSM test but fails at the handle is a failed bag, and handle strength is where most field complaints actually originate.